Separation of water vapor from a gas mixture, and subsequent condensation of the water vapor into liquid water, may be accomplished by capillary condensation. Capillary condensation may be carried out with the use of a module having a porous substrate coated with a porous membrane. The porous membrane is designed to foster capillary condensation of water vapor from gas flowing along the porous membrane. Specifically, the porous membrane may have pores sized to receive water vapor from gas flowing along the porous membrane. The pores are sized such that, when the water vapor is in one of pores of the porous membrane, the pores confine the water vapor molecules, which increases van der Waals interactions between the water vapor molecules to ultimately result in condensation of the water vapor to liquid water. The liquid water flows into the porous substrate, and may be removed from the porous substrate with application of a vacuum.
The extent to which capillary condensation occurs is dependent on the temperature of the membrane, as identified in the Kelvin equation. Specifically, the extent to which capillary condensation occurs decreases as the temperature of the membrane increases. In applications where an increase in water removal is required, the volume of the substrate may be increased. Such an increase in volume results in an increase in manufacturing cost and an increase in packaging constraints for the module. In addition, if the thermal conductivity of the substrate is too low, then the heat release from water condensation could increase the temperature of the enlarged substrate, and reduce the extent to which capillary condensation occurs, thereby reducing substrate water collection efficiency.